CONNECTIVE TISSUE. 



255 



the original periosteum, the fibers and blood-vessels of which 

 stand at right angles to each other. 



The formation of bone from fibrous connective tissue is best 

 studied in the skull of the human embryo, at about the fourth 

 month of development. (See Fig. 105.) 



FIG. 105. SKULL OF A HUMAN EMBRYO, FOUR MONTHS OLD. 

 HORIZONTAL SECTION. CHROMIC ACID SPECIMEN. 



M, muscle-layer of the scalp ; SM, submuscular loose, freely vascularized connective tis- 

 sue ; P, dense connective tissue of external pericranium ; B, first-formed trabeculae of bone ; 

 O, layer of osteoblasts, attached to the trabecula) ; DM, dense connective tissue of internal 

 pericranium the future dura mater. Magnified 100 diameters. 



